1. Field of the Invention
This invention relates to preamplifiers used in rotating disk storage devices. In particular, this invention relates to preamplifiers incorporated into the head disk assembly in close proximity to the read/write heads associated to the data storage disks.
2. Description of the Related Art
Rotating disk data storage devices are known in which one or more read/write heads, typically inductive heads, are used to store data on and read data from an associated disk media surface. In a typical magnetic media implementation of such a storage device, a circuit element known as a "preamplifier" or "preamplifier/write driver", receives from an associated "channel" device both data signals to be written onto a disk surface during a write operation, and control signals used to specify the individual head to be selected for a read or write operation. The preamplifier/write driver also typically supplies analog data signals read from a head to the associated channel. A typical preamplifier/write driver includes a write preamplifier for conditioning the write data signals received from the associated channel, a read preamplifier for amplifying signals supplied by a read head, a multiplexer for interconnecting the data input and data output internal lines to one of a plurality of read/write heads, and a mode control unit for operating the multiplexer in response to control signals supplied from the channel, typically a chip select signal (-CS) for controlling the state of the circuitry within the preamplifier, and a read/write (R/W) signal for specifying either a read operation or a write operation.
As the complexity of disk data storage devices has increased by adding heads (and corresponding additional storage surfaces), the requirement for added functions and controls has also increased. The use of magnetoresistive (MR) read/write heads has introduced the need for further control circuitry providing the required bias current or voltage to the read portion of such heads. Additionally, MR heads double the head selection problem, having separate read and write head connections versus the use of inductive heads where a common head is used for reading and writing. Still further, the highly competitive disk drive market requires cost reduction through automating testing of drives during manufacture and in the field. Because a drive may be manufactured with a variety of head configurations supplied from multiple sources, and in fact a preamplifier/write driver circuit may be multiply sourced, an increasing sophistication in structure and function in the preamplifier/write driver design is now required to improve efficency, yield and consequently, cost in the manufacture of the drive.
The demand for additional function in the preamplifier/write driver must be satisfied within the constraints of a limited number of integrated circuit terminal pins since both cost and available circuit board space are design constraints. There is, therefore a need for a preamplifier/write driver which satisfies the demand for increasing test functions in a complex manufacturing environment while meeting the conflicting demands of cost and board space reduction.